What I would love to have is a few compact dialup-to-wifi bridges so I could wifi-ize 30 year old hardware.

Would be neat to read email with an old POP client, or chat over the original AIM software (perhaps patched to use a server on the LAN)

I've wondered for a while if it would be possible to do that with a USB FXS adapter[1], and something like a Pi, but you'd basically need a soft modem of some kind to make it work and the only module for Asterisk isn't up to the challenge (last I checked five years ago).

However, to be frank, it'd make more sense to do PPP over null modem with a straight serial connection.

[1]: https://www.amfeltec.com/usb-fxs-adapter/